VARIATION IN PEDIGREE-CULTURES 215 



difficult problems of relationship, it is becoming more and more cus- 

 tomary to secure the individuals representing the doubtful forms and 

 cultivate them under identical conditions, thus securing data for com- 

 parison and analysis, representing all stages of development of the 

 sporophyte from the seedling to the mature fruit. The record of im- 

 portant questions which have been solved in this manner is a long one, 

 and includes the investigations of Alexis Jordan on Drab a, Sargent 

 on Crataegus, Wittroek on violets. Britton and Eose on Crassulacece and 

 scores of other less extensive researches. 



If the observer becomes interested in the hereditary action of his 

 plants in addition to a comparison of their anatomical and physio- 

 logical qualities, it then becomes necessary to follow his plants from 

 generation to generation to ascertain to what extent and in what 

 manner variation may ensue. 



The first step in this work is to secure purely fertilized seeds. 

 Hybridization is not common among plants except in a few genera, 

 yet in tests which must continue for a number of years every precaution 

 must be used to ensure accuracy of results. The observer, therefore, 

 covers the unopened flower bnds of the individuals from which he 

 wishes to procure seeds with bags of paper, or other suitable tissue, and 

 then makes sure that pollination is secured spontaneously, or by band, 

 with no danger of admixture of any kind. 



In due time the ripened seeds, with photographs, notes and proper 

 herbarium material, are taken from the parental individuals. With 

 the first lot of seeds on hand, the next step is to make a pure culture 

 from them. To do this a quantity of soil of the proper consistency 

 is secured, and while in a moist condition is heated to the boiling point 

 of water in an oven on two succeeding days, or, better still, to a higher 

 temperature in an autoclav for four or five hours. The treated soil 

 may now be stored to be used as wanted, but at all times it must be 

 guarded from possible contamination by the introduction of foreign 

 seeds. 



Seed-pans, of earthenware, or shallow wooden boxes are next se- 

 cured and thoroughly washed in clean water and filled with sterilized 

 soil, after which they are set in place in a cold frame, or in a green- 

 house or germination chamber. As each pan is to be used it is taken 

 to a special operating table, and the selected seeds are sown directly 

 from the packet, so that from three to five hundred (in the case of small 

 seeds) are evenly distributed over the surface. A thin even layer of 

 earth is sifted over the seeds, a wooden label is affixed to the pan, 

 giving all necessary data, and the pan is returned to its place in the 

 culture room. If more than one species is being tested at the same 

 time, the greatest care must be used to prevent admixture, and the 

 remote separation of the pans may lie necessary. The splashing of 



